Evaporative air conditioners have found use in localities where there is a sufficient difference between the dry bulb temperature and the corresponding wet bulb temperature to provide a desirable heat transfer gradient without need for altering the moisture content of the useful air or for resorting to vapor compression refrigeration. For example, if the dry bulb temperature is 93.degree. F and the corresponding wet bulb temperature is 70.degree. F, there is a difference of 23.degree. F available for air conditioning operation. Early coolers operated by evaporating water directly into the useful air, thereby increasing its moisture level, but subsequent coolers have been based on the fact that the occupants of an enclosure will experience a greater degree of comfort by cooling the air of the enclosure while maintaining, or reducing, its moisture content.
A variety of sophisticated designs have been proposed and utilized wherein the heat absorptive action of evaporation is employed to reduce the temperature of heat exchange apparatus and in which air is then passed through the apparatus for the purpose of cooling. The air that is used for effecting the evaporation (working air) is conducted to the outside of the room to be cooled and the air that is cooled by passing through the apparatus (useful air) is directed into the room. In this way, the heat abstracted from the liquid during the evaporation is not redelivered to the air of the room, nor is the moisture content of the useful air increased. In this regard, one can refer to the following U.S. Pat. Nos. Re. 17,998, 2,044,352, 2,150,514, 2,157,531, 2,174,060, 2,196,644, 2,209,939, 2,784,571 and 3,214,936. Additional patents of interest are: U.S. Pat. Nos. 1,542,081, 2,488,116 and 3,025,685. In more recent years, evaporative coolers have been replaced by vapor compression refrigeration units in which refrigerant fluid is alternately compressed and evaporated in a refrigeration cycle. Such units can be made quite compact, but are generally inefficient and, importantly, energy-intensive. Dwindling energy resources have required priorities in this regard to be reexamined and the need for improved, more efficient cooling devices has become evident.
The present invention satisfies the foregoing need in that it provides a highly efficient apparatus for cooling of air. The device operates more efficiently by a conjunction of features. Specifically, a heat exchanger is used that separates its dry and wet sides; evaporating water is kept separate from the useful air so that cooling is performed without the addition of water vapor to the useful air. Additionally, the major portion, preferably all, of the working air, is drawn from the load; i.e., the working air is recirculated from the enclosure to be cooled to the wet side of the heat exchanger. Furthermore, in a preferable mode of construction, the wet side of the heat exchanger operates by movement of the working air internally through conduits countercurrently to water flowing downwardly therethrough along the conduit inner surfaces, while the useful air passes through the dry side externally across the conduits.
Specific constructional details for maximum efficiency are given hereinafter. In a specific embodiment, additional increases in efficiency can be obtained by flowing the moisture-laden return air exhausting from the wet side of the heat exchanger in heat-exchange, but separated, relationship with fresh air flow upstream from the dry side of the heat exchanger. In a further embodiment, a composite, hybrid system is provided in which a minor portion only of the useful air, downstream of the dry side of the heat exchanger, is passed over the evaporator of a vapor compression refrigeration system. A sufficiently small amount of the useful air can thus be cooled sufficiently below its dew point to dehumidify that portion of the air resulting in a greater reduction in the dry bulb temperature of the useful air. Other features are provided which, while decreasing somewhat from the total efficiency of the basic system, provide a greater degree or rate of cooling than heretofore possible with evaporative coolers for specialized applications and/or for high cooling rate usage. In this regard, a particular embodiment calls for a portion of the returned air to be diverted to mix with the fresh air for further cooling by the heat exchanger. In another particular embodiment, useful under certain climatic conditions to provide a lower temperature but at higher energy levels, a portion of the cooled useful air emerging from the heat exchanger is diverted to mix with the working return air for countercurrent contact with the evaporating water.